5V Relays and stepper motors.


I have managed to build my own PiCar based on RC-car parts (but the only things that have left are wheels, motors and wheelframe ;) ). I am using PicoBorg and 4x 5v relays to run forward/reverse main motor and motor for turning.
I know that on 2 output on PicoBorg it is possible to control speed of motor but in my solution it is not working - till about half of range motor isn't working, and after this half it is running with full power.

Maybe it is stupid question but it is possible to control power on stepper engine using these 5v relays? :)

Thanks in advance

piborg's picture

The speed control is performed using a technique called Pulse Width Modulation (PWM)

In simple terms PWM works by turning the output on and off at a fast rate, simulating a reduced voltage.

The trouble is the relays react very slowly.
In other words they cannot keep up with the on / off changes from the PicoBorg and either stay on all of the time or stay off all of the time.

In summary the relays are not suitable for controlling the power to a motor.

If you want a better explanation of PWM check out this video: Circuit Skills: PWM.
For a detailed explanation see the Pulse Width Modulation Wikipedia page.

So I need to get some money and buy PicoBorg Reverse to avoid relays(am I right? :) ) Thank you very much for quick answer and clarifying this! :)

piborg's picture

A PicoBorg Reverse would be capable of doing what you require, allowing the direction and power control without the need for the relays.

Glad to be helpful :)

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